1. Field of the Invention
The invention relates to new methine dyes, to novel intermediates useful in preparing such dyes, and to silver halide photographic compositions containing such dyes.
As used herein, the term "methine dye" means a dye comprising two nuclei, at least one of which is a heterocycle containing at least one nitrogen atom, the two nuclei being joined by a methine linkage, which is a conjugated chain of carbon atoms. Methine dyes include such dyes as cyanine, hemicyanine, and merocyanine dyes.
2. Description Relative to the Prior Art
Methine dyes are generally known, as is the use of such dyes as spectral sensitizers in silver halide photographic compositions. See, for example, Mees and James, The Theory of the Photographic Process, 3rd ed., N.Y., Macmillan, 1966, Chapter II, pp. 198-223, by L. S. G Brooker, Sensitizing and Desensitizing Dyes, 65-27328.
There is a constant search in the photographic art for new methine dyes to complement those already in use as spectral sensitizers. The present invention provides a new class of methine dyes. They have been found, unexpectedly, to be useful as spectral sensitizers for silver halide photographic compositions and thus provide the photographic chemist with a wider and more flexible choice of spectral sensitizers for any composition or process in which spectral sensitizing dyes are advantageously employed.